EXPERT TESTIMONY
Testimony about a scientific, technical, or profes-
sional issue given by a person qualified to testify
because of familiarity with the subject or special
training in the field.
Generally speaking, the law of evidence in
both civil and criminal cases confines the testi-
mony of witnesses to statements of concrete facts
within their own observation, knowledge, and
recollection. Testimony must normally state facts
perceived by the witnesses’ use of their own
senses, as distinguished from their opinions, infer-
ences, impressions, and conclusions drawn from
the facts. Opinion testimony that is based on facts
is usually considered incompetent and inadmissi-
ble, if the factfinders are as well qualified as the
witness to draw conclusions from the facts.
In certain instances, however, the law allows
witnesses to provide opinion evidence, and such
evidence is divided into two classes, lay opinion
and expert opinion.A lay witness may give his or
her opinion when that opinion is (1) rationally
based on the perception of the witness; (2) help-
ful to a clear understanding of the witness’ testi-
mony or the determination of a fact in issue; and
(3) not based on scientific, technical, or other
specialized knowledge within the scope of
expert testimony discussed below. Thus, lay wit-
nesses who have had an opportunity to observe
a particular vehicle in motion are normally per-
mitted to testify that it was traveling at a great
rate of speed or was going pretty fast. Lay wit-
nesses are also normally allowed to give their
opinion as to the height, weight, quantity, and
dimensions of things, even if their testimony is
not precise. By definition, a lay witness is any
witness who is not qualified to testify as an
expert on a particular subject.
Expert witnesses are persons who are quali-
fied, either by actual experience or by careful
study, to form definite opinions with respect to
a division of science, a branch of art, or a depart-
ment of trade. The law deems persons having no
such experience or training to be incapable of
forming accurate opinions or drawing correct
conclusions. Thus, if scientific, technical, or
other specialized knowledge will assist the trier
of fact to understand the evidence or to deter-
mine a fact in issue, a witness qualified as an
expert by knowledge, skill, experience, training,
or education,may testify in the form of an opin-
ion or otherwise, if (1) the testimony is based
upon sufficient facts or data; (2) the testimony is
the product of reliable principles and methods;
and (3) the witness has applied the principles
and methods reliably to the facts of the case. In
Kumho Tire Co. v. Carmichael, 526 U.S. 137, 149-
152, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999), the
U.S. Supreme Court further observed that the
reliability of a scientific technique may turn on
whether the technique can be and has been
tested; whether it has been subjected to peer
review and publication; and whether there is a
high rate of error or standards controlling its
operation.
Courts do not apply a rigid rule in determin-
ing whether a particular witness is qualified to
testify as an expert. Instead, an expert’s qualifica-
tions are normally evaluated on a witness-by-wit-
ness basis, according to the facts and issues of
each case. Several courts have stated that the true
criterion in determining the qualification of
expert witnesses is not whether they employ their
knowledge and skill professionally or commer-
cially, but whether the jury can receive apprecia-
ble help from them on the particular subject in
issue. Many courts also require the witness to
exhibit sufficient knowledge of the subject matter
before his or her opinion to go to the jury.
The qualifications of an expert witness must
be carefully scrutinized by courts to guard
against charlatans who may give erroneous testi-
mony without a sound foundation. Most courts
will more closely scrutinize the qualifications of
witnesses seeking to testify as experts if they
have never been found qualified to give expert
testimony on a prior occasion. However, pri-
mary reliance is not placed on the fact that it
may be the expert’s first time on the witness
stand. Conversely, the fact that a witness has
been previously qualified to give expert testi-
mony on the subject matter in question is typi-
cally irrelevant to his or her qualifications for
giving such testimony in a subsequent case.
There are two general classes of matters as to
which expert testimony is admissible: (1) mat-
ters as to which the conclusions to be drawn by
the jury depend on the existence of facts that are
not common knowledge and that are specifically
within the knowledge of persons whose experi-
ence or study enables them to testify with
authority on the subjects in question; and (2)
